Bottom Line:
Cellular toxicity and selectivity were responsible for the exclusion of 78% of the pre-selected compounds.The activity of the remaining 124 compounds was confirmed against the intramacrophagic amastigote form of the parasite.In vitro microsomal stability and cytochrome P450 (CYP) inhibition of the two most active compounds from this screening effort were assessed to obtain preliminary information on their metabolism in the host.

ABSTRACTDrugs currently available for leishmaniasis treatment often show parasite resistance, highly toxic side effects and prohibitive costs commonly incompatible with patients from the tropical endemic countries. In this sense, there is an urgent need for new drugs as a treatment solution for this neglected disease. Here we show the development and implementation of an automated high-throughput viability screening assay for the discovery of new drugs against Leishmania. Assay validation was done with Leishmania promastigote forms, including the screening of 4,000 compounds with known pharmacological properties. In an attempt to find new compounds with leishmanicidal properties, 26,500 structurally diverse chemical compounds were screened. A cut-off of 70% growth inhibition in the primary screening led to the identification of 567 active compounds. Cellular toxicity and selectivity were responsible for the exclusion of 78% of the pre-selected compounds. The activity of the remaining 124 compounds was confirmed against the intramacrophagic amastigote form of the parasite. In vitro microsomal stability and cytochrome P450 (CYP) inhibition of the two most active compounds from this screening effort were assessed to obtain preliminary information on their metabolism in the host. The HTS approach employed here resulted in the discovery of two new antileishmanial compounds, bringing promising candidates to the leishmaniasis drug discovery pipeline.

pntd-0000675-g005: New quinoline with antileishmanial activity.Unlike other quinoline derivatives reported as antileishmanial compounds, CH872 contains a 4-OH group that allows this compound to equilibrate with its tautomer (CH872A). 8-Cl can facilitate the tautomerization by making a H-bond with the NH in CH872A.

Mentions:
The most active compound, CH872, is of interest due to its high in vitro activity and lack of cytotoxicity (Fig. 3, Table 1 and Figure S2), along with favorable metabolic stability and CYP inhibition data (Table 2). Additionally, its core structure, 4-hydroxyquinoline, is a novel scaffold for antileshmanial inhibition. Several modifications of quinolines have been carried out to obtain antileishmanials, such as sitamaquine or quinoline derivatives with side-chains at C4 or at phenyl rings [32], [33]; however, none of these modifications produced 4-hydroxyquinoline derivatives. Sitamaquine is in clinical trials (Phase II), and no other quinoline derivatives have been approved as antileishmanial drugs. Some issues reported from this class of compounds include kidney toxicity, which can be lethal [34]. Unlike other antileishmanial quinoline derivatives, compound CH872 contains a 4-OH group, which allows this compound to equilibrate with its tautomer CH872A (Fig. 5). Studies directed toward establishing the structure-activity relationships (SARs) and defining the mode of action of CH872 are currently underway.

pntd-0000675-g005: New quinoline with antileishmanial activity.Unlike other quinoline derivatives reported as antileishmanial compounds, CH872 contains a 4-OH group that allows this compound to equilibrate with its tautomer (CH872A). 8-Cl can facilitate the tautomerization by making a H-bond with the NH in CH872A.

Mentions:
The most active compound, CH872, is of interest due to its high in vitro activity and lack of cytotoxicity (Fig. 3, Table 1 and Figure S2), along with favorable metabolic stability and CYP inhibition data (Table 2). Additionally, its core structure, 4-hydroxyquinoline, is a novel scaffold for antileshmanial inhibition. Several modifications of quinolines have been carried out to obtain antileishmanials, such as sitamaquine or quinoline derivatives with side-chains at C4 or at phenyl rings [32], [33]; however, none of these modifications produced 4-hydroxyquinoline derivatives. Sitamaquine is in clinical trials (Phase II), and no other quinoline derivatives have been approved as antileishmanial drugs. Some issues reported from this class of compounds include kidney toxicity, which can be lethal [34]. Unlike other antileishmanial quinoline derivatives, compound CH872 contains a 4-OH group, which allows this compound to equilibrate with its tautomer CH872A (Fig. 5). Studies directed toward establishing the structure-activity relationships (SARs) and defining the mode of action of CH872 are currently underway.

Bottom Line:
Cellular toxicity and selectivity were responsible for the exclusion of 78% of the pre-selected compounds.The activity of the remaining 124 compounds was confirmed against the intramacrophagic amastigote form of the parasite.In vitro microsomal stability and cytochrome P450 (CYP) inhibition of the two most active compounds from this screening effort were assessed to obtain preliminary information on their metabolism in the host.

ABSTRACTDrugs currently available for leishmaniasis treatment often show parasite resistance, highly toxic side effects and prohibitive costs commonly incompatible with patients from the tropical endemic countries. In this sense, there is an urgent need for new drugs as a treatment solution for this neglected disease. Here we show the development and implementation of an automated high-throughput viability screening assay for the discovery of new drugs against Leishmania. Assay validation was done with Leishmania promastigote forms, including the screening of 4,000 compounds with known pharmacological properties. In an attempt to find new compounds with leishmanicidal properties, 26,500 structurally diverse chemical compounds were screened. A cut-off of 70% growth inhibition in the primary screening led to the identification of 567 active compounds. Cellular toxicity and selectivity were responsible for the exclusion of 78% of the pre-selected compounds. The activity of the remaining 124 compounds was confirmed against the intramacrophagic amastigote form of the parasite. In vitro microsomal stability and cytochrome P450 (CYP) inhibition of the two most active compounds from this screening effort were assessed to obtain preliminary information on their metabolism in the host. The HTS approach employed here resulted in the discovery of two new antileishmanial compounds, bringing promising candidates to the leishmaniasis drug discovery pipeline.